This invention relates to optical disk apparatuses used with replaceable optical disks each accommodated in a cartridge and, more particularly, to an optical disk apparatus, in which an optical head objective lens is cleaned using a cleaning disk.
In a usual optical disk apparatus, information is recorded by projecting a beam from a laser diode onto a rotating optical disk. The recorded information is reproduced through detection of changes in the intensity of the reflected beam from the optical disk, polarization surface and other characters. Such optical disk apparatus provides for high information recording density, and thus its applications to external memories of information processing systems are expected.
Normally, a laser beam emitted from the laser diode is focused by an objective lens provided on an optical head mounted on a carriage onto the optical disk. The reflected beam from the optical disk is also focused by the objective lens to be incident on a light-receiving element for conversion to an electric signal. The objective lens is driven for focus control by a lens actuator in the optical axis directions. Further, the carriage carrying the optical head is by a voice coil motor in radial directions of the disk for position control of the optical head to a desired position. The objective lens is found close to the disk surface, typically several millimeters apart. Therefore, its surface is readily contaminated by winds produced by the rotation of the optical disk. Contamination of the objective lens surface results in reduction of the laser beam intensity, scattering of the beam and disturbance of the laser beam intensity distribution, thus having significant adverse effects on the write performance, the read performance and further the servo performance such as focus servo and track servo. A method of cleaning the objective lens surface uses a cleaning disk. With the cleaning disk, the cartridge case and disk resemble those of the normal optical disk cartridge. A difference is that the cleaning disk has a brush provided on part of its surface. The cartridge accommodating the cleaning disk, like the normal optical disk cartridge, is loaded in the apparatus, and the disk is rotated, whereby the objective lens surface is cleaned by the brush on the disk.
However, in the cleaning of the objective lens with such a cleaning disk, the objective lens is held stationary, and its surface is rubbed by the brush of the rotating disk. This means that only part of the brush can be used for the cleaning. Therefore, the brush is liable to be deformed, and also it is contaminated only locally. Further, the rotating brush touches the stationary objective lens in a fixed fashion, and therefore the lens can not be perfectly cleaned.
Meanwhile, when writing data in the optical disk, the desired track is first erased by projecting a laser beam thereonto in the presence of an external magnetic field applied in the erase direction. Then, data is written by projecting a data-modulated laser beam in the presence of an external magnetic field applied in the write direction. Further, a verify read is done to confirm the written content. Therefore, with an optical head which projects a single laser beam, the optical disk has to be rotated by at least three rotations in the write operation. To permit this write operation at an increased speed, there is provided an optical disk apparatus, which has three exclusive laser diodes for erasing, writing and reading, and in which two objective lenses, one for erasing and the other for writing and reading, are mounted together with respective lens actuators on the optical head. With such a two-actuator structure optical disk apparatus, the erase, write and read operations can be performed during one rotation of the disk, and thus the write operation speed can be increased by three times compared to the case of the ordinary optical disk apparatus. However, in such a two-actuator optical disk apparatus the two lens actuators are disposed in the same radial position of the disk and considerably close to the disk in the circumferential direction thereof. Therefore, the cleaning of the succeeding objective lens with the cleaning disk with the brush is obstructed by the preceding one. Therefore, unlike the single-lens structure, the lenses can be cleaned only insufficiently.